Machines, for example, motor graders, dozers, compactors, pavers, and profilers to name a just a few, are used for geographic surface altering operations. Such machines typically operate at construction sites which were previously manually surveyed, and staked according to construction site plans. During the process the construction site is frequently checked in order to confirm that the processed site meets the design specifications. This process requires large amounts of manual labor much of which is by highly trained personnel. Further, the machine operator must be highly trained in order to obtain the degree of accuracy required.
Laser systems have been in used in some applications to provide a reference for the operator to follow. A laser beam emitted by a laser positioned at a surveyed location on the site is swept over the site. This establishes a laser plane. A receiver on the machine receives the laser beam and indicates to the operator the elevational position of the beam relative to a location on the machine, such as the machine or implement. This information is used by the machine operator for machine controlling purposes. An example of one such system is shown in U.S. Pat. No. 4,807,131 dated Feb. 21, 1989, to Philip M. Clegg. This patent discloses measuring the elevational position of the grading blade relative to the laser plane and displaying on a monitor parameters such as target elevation, actual elevation, and an allowable range of error so that the operator can, in one mode of operation, adjust the blade position to be within tolerance of the target location.
Implements are normally adjustably connected to the machine frame so that the slope, pitch, and elevation of the work implement can be varied relative to the machine. When the laser receiver is mounted on the machine frame any change in the position of the work implement relative to the frame causes an unaccounted for change in the position of the work implement relative to the plane and the receiver. The information therefore provided to the operator is less than desirable and may not be used to any significant advantage. Placing a single laser receiver on the work implement eliminates this problem to the extent that the laser receiver moves with the work implement and is related to work implement position. However, any changes in tilt, pitch or rotation of the work implement relative to the laser plane are not compensated for and therefore the information provided is still not accurate.
Placing two laser receivers on the implement permits the slope of the blade to be determined relative to the laser plane however this does not allow for the change in position of the implement caused by implement tipping (pitching).
Systems are known which use a constellation of satellites and a special receiver to determine by triangulation the position of a machine (actually the position of the antenna) in three space coordinates relative to a work site coordinate system. Such systems are normally referred to as a kinematic global positioning systems (GPS). Historically, such systems have not been widely accepted since the accuracy of position determination was less than satisfactory for certain applications. Further, slow processing time reduced the commercial feasibility of determining machine position in realtime. Over the past few years the accuracy of position determination has been improved and the speed of processing has been increased. Thus, the potential to determine the realtime position of a machine is now feasible for an assortment of applications including, for example, geographic surface altering machines.
However, one of the problems currently still associated with GPS receivers is the occurrence of periods of time when the GPS data is invalid. There may be several reasons for this occurrence, including obstructions which block the satellite signals or lack of enough satellites in view of the GPS receiver to obtain a good position signal.
The present invention is directed to overcoming one or more of the problems as set forth above.